1. Field of the Invention
This invention relates to air-conditioning systems, and more particularly to air-conditioning systems that include a compressor operated with an electric motor and an engine.
2. Description of the Related Art
Compressors may operate within a refrigeration system, such as an air-conditioning system, to create cooling capacity by compression of a working fluid. A compressor typically includes a pulley that is rotated by a driving force to create compression. In a vehicle, such as an automobile, an engine that also provides for movement of the vehicle may supply the driving force. Alternatively, the driving force can be supplied by an electric motor energized by a battery or other device capable of generating electrical energy.
A type of compressor known as a variable displacement compressor may be controlled to provide varying amounts of compression. The compression may be varied depending on the cooling capacity needed. Varying the amount of compression also varies the amount of driving force needed to rotate the compressor. In a non-variable displacement compressor, the compression is fixed.
In some applications, the engine or the electric motor may selectively rotate the compressor. In these applications, the driving force provided by the electric motor or the engine is sufficient to rotate the compressor. In other applications, where a variable displacement compressor is used, the electric motor may be sized to provide less than the driving force necessary to rotate the variable displacement compressor when maximum compression is desired. In this configuration, the electric motor is only activated when the driving force that is required is below a predetermined threshold and otherwise the engine provides the driving force. Upon starting the electric motor in any of the above applications, sufficient driving force must be provided by the electric motor to initiate the rotation of the compressor.
A known problem with electric motors is the potential for high inrush current when the motor is first energized from a stopped condition. The amount of inrush current is affected by the amount of starting torque, or driving force, required to initiate rotation of the electric motor. High inrush current requires the electric motor, conductors feeding the electric motor and a switch that activates and deactivates the electric motor to be sized to avoid damage due to the inrush current. In addition, an energy source supplying the electric motor is required to have sufficient capacity to supply the high inrush current. Further, the high inrush current may decrease the longevity of the supply from a battery or other similar energy source.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the embodiments described below include a method and system for operating an air-conditioning system using an engine and an electric motor. The engine and the electric motor may be selectively activated to sustain operation of the air-conditioning system.
The operation of the air-conditioning system may be sustained by the electric motor during times when the engine is turned off. The engine and the electric motor are operable to selectively rotate a compressor in the air-conditioning system. During operation, when the engine is selected to rotate the compressor, the engine also rotates the electric motor. When the engine stops operating, the electric motor may be synchronously activated to maintain continuous rotation of the compressor thereby minimizing inrush current of the electric motor.
In an alternative embodiment, the compressor is a variable displacement compressor. In this embodiment, the engine and electric motor cooperatively operate as previously discussed. The electric motor may be sized to operate throughout the range of the variable displacement compressor. Alternatively, the electric motor may be sized to provide only enough driving force to operate the variable displacement compressor when the variable displacement compressor is not fully loaded. As such, the electric motor may only be activated when the load on the variable displacement compressor is below a predetermined amount and the engine stops. Since the electric motor is activated while the variable displacement compressor is still rotating, inrush current for the electric motor is minimized.
A method of sustaining operation of an air-conditioning system is described by one embodiment. The method comprises operating a compressor with an engine, operating the compressor with an electric motor and maintaining continuous operation of the compressor with the electric motor when the engine stops.
Another embodiment describes a method of sustaining cooling using an air-conditioning system. The method comprises rotating a compressor with an engine. The method further comprises activating an electric motor to rotate the compressor when a rotational speed of the electric motor is within a predetermined range of a rotational speed of the compressor. In addition, the method comprises disengaging the engine from the compressor.
Yet another embodiment describes a method of cooling using an air conditioner sustain system. The method comprises operating a variable displacement compressor with an electric motor, monitoring the loading of the variable displacement compressor, and adjusting an operating speed and a displacement of the variable displacement compressor to operate at an optimal efficiency point.
An electric air conditioner sustain system, where an engine operates a compressor within an air conditioner system is disclosed by another embodiment. The electric air conditioner sustain system comprises an electric motor coupled to the compressor and a controller electrically connected with the compressor and the electric motor. The controller is operable to activate the electric motor to maintain continuous operation of the compressor when the engine stops.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.